Di-ureasils

Fig. 105. Some components and precursors of di-ureasil inorganic-organic hybrids.

Lifetimes (ms, at 14 K) of the di-ureasils emitting centers and efficiency (%) of the energy transfer to the Nd111 ion in d-U(Y)BNd(Otf)3 xerogels percentages within parentheses indicate the Nd111 content with respect to the total mass... 

Room-temperature NIR emission has also been reported for the di-urethanesils Ut(600)3-Er(Otf)3 and Ut(900) Nd(Otf)3 ( = 80,60), indicating that this hybrid framework protects the lanthanide ions from nonradiative deactivation processes equally efficiently when compared with the di-ureasils (Carlos et al., 2004). In fact, the most noticeable difference between the Nd111-doped di-ureasils and di-urethanesils is the energy difference between the undoped host and the doped hybrids which, in the case of Ut(600) , for instance, is concentration dependent (Gongalves et al., 2005). 

Ferreira, RA.S., Brites, C.D.S., Vicente, C.M.S., Lima, PJ., Bastos, A.RJ J., Marques, P.G., Hiltunen, M., Carlos, L.D., and Andre, P.S. (2013) Photonic-on-a-chip a thermal actuated Mach-Zehnder interferometer and a molecular thermometer based on a single di-ureasil organic-inorganic hybrid. Laser Photon. Rev., 7 (6), 1027-1035. 

Pecoraro, E., Garcia-Revilla, S., Ferreira, R.A.S., Baida, R., Carlos, L.D., and Fernandez, J. (2010) Real time random laser properties of Rhodamine-doped di-ureasil hybrids. Opt. Express, 18 (7), 7470-7478. 

P.C., Evans, A., de Zea Bermudez, V., Smith, M.J., and Ostrovskii, D. (2006) Sol-gel preparation of a di-ureasil electrolyte doped with lithium perchlorate. Electrochim. Acta, 52, 1542-1548. 

Pecoraro, E Andre, P.S., and Carlos, L.D. (2011) Optical filters and resonant cavities based on di-ureasil organic-inorganic hybrids./. Sol-GelSci. Technol, 59, 475-479. 

Abstract The interest in sol-gel derived polymer/siloxane hybrid electrolytes has grown considerably during the last decade because of their potential application in sohd state electrochemical devices, in particular batteries and electrochromic devices (ECDs).This review intends to provide an overview of the latest advances in the investigation of the structure, morphology, thermal properties, electrochemical behavior and spectroscopic features of Li -coutaiuiug di-urea crosslinked polyoxyethylene (POE)/siloxane (di-ureasil) electrolytes. Applications of these materials in ECDs will be addressed. 

The doped di-ureasils are described by the d-U(Y) MX notation, where n (salt composition) represents the number of ether oxygen atoms per cation and X is the anion. For instance, the sample d-U(2000)2oLiBF4 is a long chain di-ureasil incorporating an amount of lithium tetrafluoroborate such that the Opoe/LT ratio is equal to 20. 

Figures 5.1-5.3 are included to demonstrate the effect of the choice of the di-ureasil network on the ionic conductivity. The Arrhenius plots show the variation of ionic conductivity with temperature of selected compositions of the d-U(2000)-, d-U(900)- and d-U(600)-based di-ureasU systems doped with the four lithium salts mentioned above. ...

Arrhenius conductivity piots of the d-U(2000) LiX di-ureasil systems. Adapted from Siiva et Gomes Correia... 

Typically the total ionic conductivity of the di-ureasils discussed here was measured by placing the sample between gold blocking electrodes, along the so-called electrode/di-ureasiUelectrode assembly, which was secured in a suitable constant-volume support, to form a symmetrical cell. 

Figure 5.2 compares the ionic conductivity of di-ureasil systems composed of the same host matrix. While at temperatures higher than 60 °C the d-U(900) LiC104 ormolytes are more conducting than comparable d-U(900) LiTFSl materials, at lower temperatures the difference is negligible and LiTFSl is a better choice for safety reasons. 

Comparison of the variation of Tg and of the ionic conductivity of selected compositions of three di-ureasil systems doped with UBF4 at 30 °C as a function of composition. Adapted from Barbosa et al. ... 

For the DSC measurements of di-ureasil ormolyte samples, sections have been usuaUy removed from dry films and subjected to thermal analysis under a flowing inert atmosphere between 25 and 300 °C and at a heating rate of 5°C min. Samples are then transferred to aluminium cans. 

The application of the ormolytes in electrochemical applications depends on their stability window. To evaluate the electrochemical stability window of di-ureasil ormolyte compositions we have typically used a two-electrode cell configuration involving the use of a 25 pm-diameter gold microelectrode surface. Cell assembly was initiated by locating a freshly cleaned... 

Voltammogram of d-U(2000)i5LiTFSI di-ureasil electrolyte at a 25 im diameter gold microelectrode vs. Li/Li". Initial sweep direction is anodic and sweep rate is 100 mV s. Reproduced from Barbosa... 

Hie electrochemical stability range of the lithium-doped di-ureasils was determined by microelectrode cyclic voltammetry over the potential range between -1.5 and 6.5 In the anodic region, all ormolytes are stable... 

Infrared and Raman spectroscopy are powerful tools in the elucidation of the ionic conductivity/ionic association relationship in PE systems. This sort of spectroscopic analysis usually involves the examination of diagnostic bands of the host polymer and of the anion. In the case of the organic/ inorganic hybrid matrices incorporating organic cross-links (e.g. di-ureasils), this study must also include the analysis of the bands characteristic of these functional groups (i.e. urea groups). 

A typical procedure adopted to monitor the coordination of cations to POE chains, based on the inspection of the skeleton vCOC modes in the FT-IR spectra, follows. The example given deals with a study previously carried out by our group on d-U(2000) LiCF3S03 di-ureasil ormolytes. In the... 

FT-IR vCOC region of selected d-U(2000) LiCF3S03 di-ureasils (a) and results of the curve-fitting results for the most concentrated samples (b). Adapted from Nunes et a . ... 

Room temperature FT-Raman spectra of d-U(2000) LiCF3S03 di-ureasils in the rCFl2 region. Reproduced from Nunes et... 

Three examples of these analyses will be given as follows. The first case mentioned here will be the spectroscopic study of the d-U(2000)-based di-ureasil system doped with LiCFsSOs. We will then refer a spectroscopic study of the d-U(2000)-based di-ureasil system doped with LiTFSI. Our third example is very recent and deals with d-U(2000)-based di-ureasil networks doped with LiBF4. ... 

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